The overall goal of this application is to study the feasibility of using the prototypical progesterone receptor modulator mifepristone, also known as "RU486," for ovarian cancer therapeutics. Ovarian cancer is the leading cause of death in women from gynecologic diseases, in part because of the difficulty in performing early diagnosis, and also due to the lack of successful treatment strategies. Treatment for ovarian cancer generally involves cytoreductive surgery followed by platinum-based chemotherapy, yet the major barrier that this treatment encounters is the development of chemoresistance, which leads to therapeutic failure. It is therefore clear that new therapeutic options for patients with advanced disease are desperately needed. Our preliminary data have demonstrated that mifepristone not only is a cytostatic agent for ovarian cancer cells, but also enhances the cytotoxicity of the standard chemotherapeutic agent cisplatin. These results led to the hypothesis that mifepristone can be exploited therapeutically in two manners: first as a cytostatic agent blocking the repopulation of cells that had survived chemotherapy;and second, enhancing chemotherapy-induced lethality. Specific aim 1 will identify the underlying molecular mechanism of the cytostatic effect of mifepristone in cultured ovarian cancer cells, and will test the efficacy of the compound in an in vivo setting using immunocompromised mice. Specific aim 2, using ovarian cancer cell lines of similar genetic backgrounds but carrying different sensitivities to cisplatin, will define whether mifepristone prevents repopulation of cancer cells in between rounds of cisplatin chemotherapy and the mechanism whereby it enhances cisplatin-mediated lethality. Results from this investigation have the potential for a major impact on human health because combination of mifepristone with standard cytotoxic chemotherapy would allow a reduction in the effective dose of cytotoxic drugs leading to reduced toxic side effects, lower chemoresistance and longer survival. At present there is no hormonal therapy approved for the treatment of any type of ovarian malignancy, yet the rationale of our preliminary results suggest that mifepristone is a promising hormonal therapeutic agent to be added to the list of anti-epithelial ovarian cancer drugs with the final goal of converting this lethal cancer into a treatable chronic disease.